Binding sites for Angiotensin II (AII) and Angiotensin Converting Enzyme (ACE) were studied in human adrenal glands and pheochromocytomas and in rat and bovine adrenals. In human and rat adrenals, both AII and ACE binding sites were localized in the medulla and zona glomerulosa, being absent in the rest of the cortex. In bovine adrenals, ACE binding sites were not detectable. The number of AII binding sites was higher in the zona glomerulosa, lower in the rest of the cortex and not detectable in the medulla. In human pheochromocytomas, ACE binding sites were homogeneously distributed throughout the tumor. However, AII binding sites could not been detected. These results suggest that circulating and/or locally formed AII could regulate the adrenomedullary and zona glomerulosa functions in man. Our findings also indicate that chromaffin cell tumors retain their ACE binding sites while losing their AII binding sites. These results indicate alterations in the regulation of the renin-angiotensin system in chromaffin tumors.